Underwater concrete repair of slab

[wetengineer]

I have a boat ramp that extends underwater. The last section, 2' under the waterline, is broken up and needs to be replaced. Anyone have any experience pouring concrete under 2' of water? (The area in need of repair is about 2' x 3') Is this possible, and if so, any tips (mix additives, process, etc.) you could relay would be great!!

Thanks...

 

[bimr]

SlideRuleEra posted this article a few weeks ago:

"Here is a somewhat dated article (1962) that describes the traditional way for placing concrete underwater with a what is called a tremie:"

 

[ACtrafficengr]

Could you precast it in the dry, then place it with a small crane or loader?

"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

 

[Jc67roch]

Precast or a tremie will both work. There is a plastic sleeve that can be fitted to a funnel for tremie placements that are in deeper water to ensure the concrete does not "fall" thru the water and separate. I used this on a pour for a concrete base in a cofferdam about 20 feet below water. But I doubt you will need this with 2 feet of water. A short section of pipe should be sufficient. Pour the concrete thru the pipe and ensure the bottom of the pipe is always surrounded by concrete to avoid water infiltration, and hence separation of the cement and aggregate. The more difficult part may be getting a smooth(reasonable) finish on the top of the concrete. Talk to your local concrete supplier about admixtures that may help keep the concrete together until it sets. Also, depending on the water (stream, lake, pond) the local environmental agency may have requirements for you regarding avoiding contaminating the water. You may need to surround the work area with haybales anchored in the water with rebar, filter fabric, or other measures.

 

[chicopee]

What is the reason for the concrete breakin up at the edge of the ramp?

 

[wetengineer]

I believe that the freeze thaw cycles over the years caused the damage. The wave action then pulled quite a bit of soil out from under the 'good' part of the slab.

Thanks for the feedback...I think based on the size of the hole, I'll try pouring through a pipe. As far as the top goes, maybe a weighted down sheet of plywood over the pour will give me a reasonable surface (at least good enough for trailer tires).

The tremie article was helpful.

 

[PShwet]

I need to know about underwater anchoring methodology along with the machinery and material involved in it. The anchoring is to be done for the extension of existing wharf.

 

[Prepakt1]

You can pour concrete into a fabriform bag and the top will be reasonably smooth . the bag will also accomodate and flow into any large holes below the concrete. To fill deeper narrow holes you will need to use a grout tube and grout through the bags after the bags have been filled, Anchoring can be achieved by installing helical piles into the bed and manufacturing the bags with holes and with nylon cabling attached to enable them to be an intergal part of the structure.

Intrusion Prepakt /marineconcrete.com